Abstract
Foamed glass-ceramics without using foaming agent have been synthesized in a novel glass system of SrO-CaO-Al2O3-TiO2-B2O3-SiO2-P2O5-MxOy (where M=Ba, Mg, La, Ce and Ni) by a simple process of powder sintering. The glass and glass-ceramics are characterized by dilatometry, differential scanning calorimetry (DSC), heating stage microscopy (HSM), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), optical microscopy and Fourier transformed infrared spectroscopy (FTIR). All the glasses formed are amorphous and the glass transition temperature and dilatometric softening temperature of these glasses are found to be in the range 673–678°C and 706–728°C respectively. The glasses are highly stable as indicated by the DSC evaluated glass stability parameters of the range 195–240°C. Quantitative sintering study of glass powder compacts revealed swelling in the samples with NiO and CeO2 corresponding to a geometry change of 75 and 108% around 900°C respectively. With reference to this finding the glass powder compacts are heated to 900°C and the foamed glass-ceramics are obtained. Characteristic crystalline silicate phases have been identified in the XRD studies and their microstructures are recorded by FESEM. Optical microscope study of the foamed samples revealed formation of bigger foamed cavity with residual pores in samples with NiO and CeO2 in comparison to samples with BaO, MgO and La2O3. The mean pore diameters of the samples with NiO and CeO2 are determined to be 43 and 32μm, and their respective porosities are 2.34 and 1.82cm3/g respectively. Thus NiO and CeO2 are found to be very effective to obtain foamed glass-ceramics without using foaming agent by the viscous flow sintering of fine glass powder compacts along with the reduction of the respective polyvalent ions.
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